You don't need exercise equipment to build six pack abs. You can use simple bodyweight exercises and still achieve the same or even better results. Start by including static holds while doing crunches or sit ups.

Static holds are performed by holding a particular position midway during a particular movement and staying still for a period of time. Perform a static hold during a crunch by starting out doing a regular crunch as usual. As you raise your head and shoulders above the floor stop your movement at about 45 to 50 degrees from the floor and stop there for as long as you can.

Make sure that you flex your abs and breathe normally. You should then move up to complete the crunch movement. You should do the hold once on the way up and once on the way down during the crunch. Increase the duration of the hold to increase the difficulty and later on you can increase the number of positions to hold midway during the crunch to further increase the difficulty.

Plank holds can be modified by resting your feet at a level higher than your forearms. Or you can do sideways plank holds by facing sideways and resting on one forearm and one foot only. Simple household items like a thick book can be held behind your head while doing crunches and you'll effectively increase the benefits you'll gain from the workout.

Also remember to actively engage your abs when doing other non-ab workouts such as sprinting or jumping rope. You can actively flex your abs even while playing sports by just deliberately engaging them. It just requires a little mental involvement and a little practice but it goes a long way in firming up your entire midsection because your abs a re an integral part of your muscular system.